The following relates generally to the optical components used in optical communication networks, and specifically to optical tap detector devices that provide optical power monitoring and detection of optical signals.
Optical power monitors or tap detectors are widely deployed in optical networks, typically in the 1550 nm or 1310 nm wavelength ranges, as well as other wavelength ranges, in order to measure and manage the optical power of the optical signals that are being transmitted over the network. In some cases, the optical power is being measured in order to adjust the optical power to a desired level. In other cases, the intent is primarily to verify that an optical signal is present.
Typical optical power monitors or tap detectors comprise an optical tap and an optical power detector. The optical tap splits off a small portion of the optical signal. Depending on the optical power levels involved, and the amount of accuracy required, the percentage of the output signal's optical power that is split off might be 1%, 2%, 5%, or even 10%. The split-off optical signal is then directed to an optical detector device, or photo-detector, which converts the optical power to an electrical signal, from which the optical power of the signal can be determined. This information can be used by the network operator, or an intelligent network controller, to adjust the power level of the optical signal, or simply to verify that a signal is present. The remainder of the optical signal (the portion that was not split off and directed to the detector circuit) is than passed on to the rest of the network. The portion of the optical power that was split off by the optical splitter, or tap, represents a source of insertion loss to the desired/intended optical signal. Because the device passes most of the incoming optical signal, an optical tap detector may be considered to be an “in-line” device, in line with the primary optical signal path. The term “in-line” may also be used to refer to devices where the light that is exiting the device is traveling in the same direction as the light that enters the device, without being “redirected” in another direction.
In some applications of optical tap detectors, it is desirable to detect signals that are traveling down the fiber in one direction, while ignoring (i.e., not detecting) optical signals that are traveling in the reverse direction, even though they are traveling on the same fiber, or fibers. This form of tap detector can be referred to as a uni-directional tap detector.
Optical splitters or couplers are widely available components that can be used to provide the optical tap function, with a variety of tap ratios (the percentage of the incoming optical power that is split off to one output of the splitter, with the remainder of the optical power being passed to the other output). Optical power detectors or photo-detectors, such as photodiodes, are also widely available, with a variety of sensitivities. Optical tap-detectors are components that combine the functions of an optical tap, or splitter, with the optical detector. In order to minimize the size and cost of optical networking equipment, it is highly desirable to have optical tap detectors that are small, and inexpensive to manufacture, so that they may be easily integrated into more complex optical modules, or directly into optical networking equipment.